The present invention relates generally to the in situ repair of underground pipe systems, and more particularly to the repair of holes, cracks, and defective joints in underground conduits including electrical conduits and drainage pipe systems such as municipal and industrial sewer systems.
Underground sanitary sewer pipe systems are designed to convey raw sewage and waste water by gravity flow to waste water treatment facilities where the sewage is processed and the waste water is treated for return to the environment. Ideally a sewer system will convey sewage and waste water to a treatment facility without leakage or spillage, but many urban sanitary sewage systems are in a state of significant disrepair. As a result of defects in sewer pipe networks, groundwater surrounding sewer pipes can infiltrate into the sewer drainage systems, adding to the quantity of water which must be conveyed and treated, and thereby reducing the effectiveness and surpassing the capacity of waste water collection systems and treatment facilities. Sewer pipes may be surrounded by groundwater permanently, or on a seasonal, tidal, or rainfall related basis, any of which may contribute to overload of the downstream waste water collection systems and treatment facilities.
Additionally, depending on the height of the water table surrounding a sewer system, raw sewage may leak out of defective conduits such as sewer pipes into the surrounding soil.
Where leaking underground drainage pipes allow infiltration of groundwater into the pipes, soil particles are typically suspended in the groundwater and flow into the pipe, leaving voids in the soil where such suspended soil particles originated. When voids are left on the outside of the pipe, the pipe is no longer supported by surrounding soil and may sag or move, increasing the size of cracks in a pipe wall or gaps between adjacent pieces of pipe. Enlarged openings through the wall of a pipe naturally permit additional infiltration of surrounding groundwater, enlarging voids, until pipes eventually can collapse completely as a result of loss of support from surrounding soil.
Underground conduits thus eventually may include longitudinal cracks, larger holes where portions of a pipe wall have collapsed, defective joints between adjacent lengths of pipe, where lengths of pipe have shifted apart or where sealing material has been carried away from a joint, and gaps or defective seals where an interconnection of a smaller pipe with a larger pipe has been disturbed.
Other types of underground conduits such as water conduits for large swimming pools have similar problems, as do some underground conduits for electrical cables, which are intended to be kept largely dry.
Uncovering underground conduits to repair defects and replace defective piping is expensive, inconvenient, and dangerous, particularly where sewer pipes are situated beneath busy streets. Nevertheless, repair must be effected or voids in the soil structure along the pipes may become large enough to allow the formation of sinkholes or total collapse of streets located above such sewer pipes.
U.S. Pat. No. 6,416,692 teaches one method for sealing underground pipes, in which a quantity of a sealing material such as a curable grout is placed into a sewer conduit between inflated tubular liner bags which are everted (or inverted, as it is often termed in the industry) within the conduit. The sealing material is subjected to pressure between the liner bags as they are everted, and is thus forced outward through defects in the wall of the conduit and into the surrounding soil to form a seal. As each bag is everted further it covers grout-filled defects in the conduit and keeps the grout from returning through the defects into the interior. This method of sealing a pipe, however, does not provide for recovery or disposal of grout which does not move from the interior of the conduit into defects in the wall of the conduit and relies on accurate estimation the amount of needed grout to assure that defects are filled sufficiently.